Refractive eye surgery is a general term for a surgical procedure intended to improve or correct the focus of a patient""s eyes by changing the shape of the eye, thereby changing the optics by which the eye sees various images. While surgeries reshaping various portions of a patient""s eye have been employed for some time, most recently, refractive eye surgery has involved reshaping the cornea of a patient""s eye.
The cornea is the clear, front surface of the eye of a person which refracts, or bends light as it enters the eye. This light that is bent by the cornea is focused on the retina of the eye. The retina is a layer of light-sensitive cells that lines the back of the eye. The retina converts light rays incident thereon into electrical impulses. These electrical impulses are sent through the optic nerve of the person to his or her brain. In the brain, these impulses are interpreted as images. If images received by the eye and refracted or bent by the cornea are not properly focused on the retina, the eye is said to have a refractive error. Myopia (near-sightedness), hyperopia (far-sightedness), and astigmatism (distortion at both near and far distances) are terms used to describe the refractive error of an eye. These refractive errors are the result of various irregular corneal curvatures, lens curvatures, or axial eye lengths that prevent images from being focused to a single point on the eye""s retina.
In performing refractive eye surgery, an excimer laser (excited dimer) may be used to reshape the cornea, thereby enabling the cornea to properly focus received light on the retina. The excimer laser interacts with the corneal tissue of the eye utilizing a laser-tissue interaction called photoablation. In photoablation, ultraviolet laser pulses precisely etch the cornea by uncoupling various intermolecular bonds thereof, thereby removing a submicron layer of cornea under highly controlled conditions. Because there is a relative absence of thermal injury to the corneal tissue during this procedure, the corneal cells can be ablated without opacifying (rendering so that light cannot pass therethrough) adjacent tissue. Such opacification might result in the inability to see through the opacified tissue of the eye. By carefully controlling the number of pulses of the ultraviolet laser, and the diameter and location of each pulse, the corneal tissue of a patient can be resculpted as necessary in order to improve the patient""s vision.
An early procedure using such an excimer laser is called PRK (photorefractive keratectomy). In this procedure, the outer surface of a patient""s eye is acted upon by the laser to change the shape of the cornea. While this procedure has been quite effective in improving a patient""s vision, the procedure has a number of disadvantages. These include a relatively long recovery time after the procedure, discomfort for the patient during and after the procedure, possible infection of the eye after procedure, the requirement for a rigid post-operative regimen, and a limit in the type of refractive corrections that can be performed.
In an attempt to improve on the PRK procedure, a new procedure entitled LASIK, or laser-assisted in-situ keratomileusis has been developed utilizing the excimer laser for refractive surgery. This variation of the original PRK procedure has become widely accepted and is practiced by ophthalmologists worldwide. This procedure has a number of advantages over traditional PRK, including a faster recovery time, less discomfort for the patient, a lower risk of infection, a more convenient post-operative regimen, and the greatest range of refractive correction possibilities. As a result, the LASIK procedure has surpassed PRK in the number of annual procedures performed.
The LASIK procedure involves the use of the above-noted excimer laser for resculpting corneal tissue within the body of the cornea, known as the corneal stromal bed, as opposed to resculpting the surface and stroma of the cornea, as performed in the PRK procedure. In LASIK, unlike PRK, a corneal flap is created by slicing the cornea along its lamnellar plane with an instrument called a microkeratome. The flap formed by this slicing, the outermost 20 percent of the thickness of the cornea, is lifted and reflected to the side. A connecting portion, or hinge between the flap and the eye remains so that the flap does not become completely disconnected from the remainder of the cornea. The reflecting of this flap serves to expose the corneal stroma, or middle layer of the corneal anatomy, to the computer-controlled laser pulses which reshape the corneal curvature. The excimer laser then reshapes the middle layer of the cornea.
After the corneal stromal bed is acted upon by the excimer laser, the flap is placed back in its original position on the cornea. The replacement of the flap provides coverage and protection for the internal surface of the cornea acted upon by the excimer laser. After the flap has been replaced, a steady stream of fluid is introduced under the flap, thereby momentarily xe2x80x9cfloatingxe2x80x9d the flap relative to the remainder of the cornea to eliminate any small amounts of debris that may be present between the flap and the remainder of the cornea as a result of the LASIK procedure. After a sufficient amount of fluid has been introduced, a milking or xe2x80x9csqueegeexe2x80x9d procedure follows for removing this excess fluid from beneath the flap margins, or xe2x80x9cguttersxe2x80x9d. Finally, the flap gutters are further dried so as to seal and adhere the corneal flap to the remainder of the cornea. This drying is conventionally performed by applying merocel (PVA) sponge spears, one point at a time, to various positions around the circumferential edge of the corneal flap.
After the LASIK procedure, many patients"" vision returns to an uncorrected 20/20, and occasionally even better with excellent visual improvement over the first 24 hours. Occasionally, results are less impressive than expected. If there is no debris in the flap-stroma interface, and no intralamellar microfolds or wrinkles (striae) in the flap, the likelihood for an excellent result increases dramatically. Thus, a pristine initial postoperative appearance typically leads to faster visual recovery, better visual results, and a decreased chance of significant inflammatory reaction. However, the introduction of any debris or striae under or in the flap will require the flap to be lifted a second time to avoid inflammation of the eye, generation of an irregular astigmatism, or any other compromised results. The degree of flap manipulation, or the number of times the flap must be touched, moved or contacted is directly related to the generation of flap striae. Thus, the less the flap needs to be touched, the less the chance of striae being generated.
A critical step in the procedure, and a step which if performed properly greatly reduces the occurrence of striae, involves the replacement of the flap and subsequent flap and corneal stroma irrigation, drying of the space between the flap and the corneal stroma and adhesion of the flap to the corneal stroma bed. As noted above, after completion of the LASIK laser treatment, surgeons advocate irrigating between the flap and the corneal stromal bed very thoroughly at the flap-stroma interface to eliminate any debris therefrom. The introduction of this irrigating solution creates a lake of fluid, as noted above, floating the flap momentarily, so that any debris is removed therefrom. This fluid and the hinge remaining between the flap and the corneal stroma bed also guides the flap back into proper position. After being properly replaced, as also noted above, the next step in the procedure involves removing the liquid from the interface between the flap and the stroma of the cornea. This process is performed by milking or squeegeeing of this fluid with a moist merocel (PVA) sponge over the surface or epithelium of the cornea and corneal flap. A sponge is placed in the middle of the cornea, and is passed over the corneal flap to the outer surface thereof to force the liquid from beneath the flap. This process is performed a plurality of times as necessary to remove fluid from beneath the flap. Other variations which perform a similar function of applying pressure to the flap surface to remove fluid from under the flap include the use of a flap applanator or the use of a corneal compressor, as is well-known in the art.
However, it is this step involving contact with the surface of the flap that is fraught with danger. First, any of the sponges or instruments that are dragged across the corneal epithelium may create a corneal abrasion, and sometimes may even puncture the corneal epithelium entirely. The result of such an abrasion or puncture of the cornea is painful, and the eye may be prone to infection. Additionally, such an abrasion can produce unpredictable visual outcomes which are less successful than desired. In addition, whether a sponge or other instruments are used in this procedure, the milking process involves depressing the delicate corneal flap, dramatically increasing the chances of generating striae therein, or other problems with the flap, thereby further adversely affecting refractive outcome.
After the milking or squeegee process has been completed, further drying is typically required circumferentially around the flap margins to encourage adhesion of the flap to the underlying stroma of the cornea. This is customarily achieved by gently applying a dry merocel sponge spear one point at a time to the entire approximately 270xc2x0 margin circumference, thereby wicking any residual fluid therefrom. This is a time-consuming, tedious process that involves multiple touches to the flap margin to remove the fluid therefrom. Because of these multiple touches to the flap, damage around the edge surface thereof, or the generation of striae therein are possible. Furthermore, the flap may shift out of alignment before adhesion as a result of these touches, once again reducing the success of the refractive outcome of the surgery. Therefore, it would be beneficial to provide a method and apparatus for removing excess liquid from under the corneal flap, while reducing the required level of manipulation of the corneal flap and direct contact with the corneal flap.
It is therefore an object of the invention to provide an improved method and apparatus for wicking fluid from underneath a corneal flap during the performance of a LASIK surgery procedure.
Another object of the invention is to provide an improved liquid wicking method and apparatus that removes excess liquid from under a corneal flap after LASIK surgery has been performed without coming into direct contact with the corneal flap, and without moving the corneal flap.
A further object of the invention is to provide an improved method and apparatus for insuring proper adhesion between a corneal flap and the remainder of the corneal stroma bed after LASIK surgery has been performed by removal of liquid from under the corneal flap until the interface between the corneal flap and the remainder of the cornea is dry, without making contact with the corneal flap.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specifications and the drawings.
A method and apparatus, in accordance with the invention for removing liquid from under a corneal flap replaced after LASIK surgery, is provided that allows for the removal of this liquid without contact between the instrument and the corneal flap. In a first embodiment, the instrument comprises a handle with a sickle-shaped end forming approximately 270xc2x0 of a circle. One face of the sickle-shaped end of the instrument has a merocel PVA sponge attached thereto and conforming to the shape of the 270xc2x0 sickle-shaped end of the instrument. During use, the diameter of sickle-shaped end of the instrument is provided to be the same or slightly larger than the typical circumference of a corneal flap produced during LASIK surgery. A handle thereof may be provided at any desired angle to the plane of the sickle-shaped end of the instrument to aid in the manipulation thereof.
After surgery, the sickle-shaped end of the instrument, including the merocel sponge, is placed adjacent to the cornea of a patient to form a 270xc2x0 crescent just slightly larger than outside circumference of the corneal flap. By capillary action, liquid from under the corneal flap is drawn into the merocel sponge. In this manner, liquid can be removed from under the corneal flap without contacting the corneal flap, thereby improving results of LASIK surgery.
In an alternative embodiment, rather than having the sponge merely conform to the sickle-shaped portion of the instrument, extended portions of the sponge material are provided to extend across a user""s conjunctiva to allow for the removal of excess liquid. More liquid may be removed and held by the apparatus of this alternative embodiment so that only one instrument need be used for each eye.
In a further alternative embodiment, rather than including a 270xc2x0 sickle-shaped end, the instrument of this embodiment includes a semi-circular end of approximately 180xc2x0, and is provided with a merocel sponge on either side of the semi-circular instrument substantially parallel to the plane thereof. Thus, the sponge on one side of the semi-circular end of the instrument can be used for removing liquid from under one side of the corneal flap, and thereafter the instrument can be flipped over and the sponge on the other side of the semi-circular end of the instrument can be used to remove liquid from the other side of the corneal flap.